A number of devices have been developed to perform non-destructive inspection of objects. For example, U.S. Pat. Nos. 5,505,090 and 5,616,865 issued to Webster, the contents of each of which are herein incorporated by reference, disclose a device for non-destructively inspecting faults in or beneath the surface of structures, such as debonds or delaminations in composite materials, cracks, broken stringers, and delaminations and the like in semi-monocoque structures. The device includes a spark gap discharge mechanism that is displaced from the object to be inspected. The spark gap discharge mechanism focuses an acoustic pulse onto a small local area of the object for vibrationally exciting the object surface. A laser Doppler camera system, also displaced from the inspection object directs a laser beam onto the excited area and derives, from the reflected light energy, the velocity of the out-of-surface displacement and relaxation frequencies generated by the surface of the excited area which are indicative of whether a fault is located in the area.
A variety of different analysis algorithms may be employed to analyze the reflected light data. U.S. Pat. No. 5,679,899 issued to Webster et al., the contents of which are herein incorporated by reference, discloses a method and apparatus for non-destructive inspection of structures that utilizes a Fast Fourier Transform (FFT) in the analysis process. The FFT is constructed for each sample point and an analysis made to set aside FFT's deviating from a pre-selected standard that represents damaged or other anomalous areas. The remaining FFT's represent an average or statistical EFT spectrum of the undamaged or fault-free area. The average FFT's and the deviating FFT's are then subtracted to provide a clear and unambiguous signal of the fault and other anomalous areas in the structure under inspection.
Each of the above-referenced patents discusses the use of an X-Y scan control system to scan the acoustic pulse generated by the spark gap across a portion of the object to be inspected. The scanning ability, however, is limited to a rather small area of the object under inspection. Accordingly, if large objects or structures are to be inspected, the device must be constantly repositioned and re-calibrated.
In view of the above, it would be beneficial if an automated device and method could be provided that would enable rapid, remote and non-contact inspection of large objects, utilizing non-destructive inspection techniques, that would not require continuous manual repositioning of the inspection equipment.